Vertical field effect transistor with reduced gate to source/drain capacitance

ABSTRACT

A method of forming a fin field effect transistor device is provided. The method includes forming a vertical fin layer on a bottom source/drain layer, and forming one or more fin templates on the vertical fin layer. The method further includes forming a vertical fin below each of the one or more fin templates. The method further includes reducing the width of each of the vertical fins to form one or more thinned vertical fins, wherein at least a portion of the fin template overhangs the sides of the underlying thinned vertical fin. The method further includes depositing a bottom spacer layer on the bottom source/drain layer, wherein the bottom spacer layer has a non-uniform thickness that tapers in a direction towards the thinned vertical fins.

BACKGROUND Technical Field

The present invention generally relates to fin field effect transistor(FinFETs) devices, and more particularly to vertical transport FinFETs.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the device channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and FinFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the FinFET can be an upright slab of thin rectangularsilicon (Si), commonly referred to as the fin with a gate on the fin, ascompared to a MOSFET with a single gate parallel with the plane of thesubstrate. Depending on the doping of the source and drain, an n-FET ora p-FET can be formed. Two FETs also can be coupled to form acomplementary metal oxide semiconductor (CMOS) device, where a p-channelMOSFET and n-channel MOSFET are coupled together.

SUMMARY

In accordance with an embodiment of the present invention, a method offorming a fin field effect transistor device is provided. The methodincludes forming a vertical fin layer on a bottom source/drain layer,and forming one or more fin templates on the vertical fin layer. Themethod further includes forming a vertical fin below each of the one ormore fin templates. The method further includes reducing the width ofeach of the vertical fins to form one or more thinned vertical fins,wherein at least a portion of the fin template overhangs the sides ofthe underlying thinned vertical fin. The method further includesdepositing a bottom spacer layer on the bottom source/drain layer,wherein the bottom spacer layer has a non-uniform thickness that tapersin a direction towards the thinned vertical fins.

In accordance with another embodiment of the present invention, a methodof forming a fin field effect transistor device is provided. The methodincludes growing a bottom source/drain layer on a substrate, and growinga vertical fin layer on the bottom source/drain layer. The methodfurther includes forming one or more fin templates on the vertical finlayer, and forming a vertical fin below each of the one or more fintemplates. The method further includes reducing the width of each of thevertical fins to form one or more thinned vertical fins, wherein atleast a portion of the fin template overhangs the sides of theunderlying thinned vertical fin. The method further includes depositinga bottom spacer layer on the bottom source/drain layer, wherein thebottom spacer layer has a non-uniform thickness that tapers in adirection towards the thinned vertical fins.

In accordance with an embodiment of the present invention, a fin fieldeffect transistor device is provided. The fin field effect transistordevice includes a bottom source/drain layer on a substrate, and one ormore thinned vertical fins on the source/drain layer. The fin fieldeffect transistor device further includes a bottom spacer layer on thebottom source/drain layer, wherein the bottom spacer layer has anon-uniform thickness that tapers in a direction towards each of the oneor more thinned vertical fins. The fin field effect transistor devicefurther includes a gate dielectric layer on the bottom spacer layer andsidewalls of each of the one or more thinned vertical fins.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional side view showing a bottom source/drainlayer formed on a substrate, in accordance with an embodiment of thepresent invention;

FIG. 2 is a cross-sectional side view showing a vertical fin layer onthe bottom source/drain layer, and a plurality of fin templates formedon the vertical fin layer, in accordance with an embodiment of thepresent invention;

FIG. 3 is a cross-sectional side view showing a plurality of verticalfins formed on the bottom source/drain layer with the fin templates onthe vertical fins, in accordance with an embodiment of the presentinvention;

FIG. 4 is a cross-sectional side view showing a plurality of thinnedvertical fins formed on the bottom source/drain layer with the fintemplates on the vertical fins, in accordance with an embodiment of thepresent invention;

FIG. 5 is a cross-sectional side view showing a non-uniform thicknessbottom spacer layer formed on the bottom source/drain layer, inaccordance with an embodiment of the present invention;

FIG. 6 is a cross-sectional side view showing a gate dielectric layerformed on the exposed surfaces of the thinned vertical fins and variablethickness bottom spacer layer, in accordance with an embodiment of thepresent invention;

FIG. 7 is a cross-sectional side view showing a gate fill layer formedon the gate dielectric layer, where the gate fill layer fills in abottom wedge region formed by the variable thickness bottom spacerlayer, in accordance with an embodiment of the present invention;

FIG. 8 is a cross-sectional side view showing a variable thickness topspacer layer formed on the gate fill layer and gate dielectric layer, inaccordance with an embodiment of the present invention;

FIG. 9 is a cross-sectional side view showing top source/drains formedon each of the vertical fins, where the top source/drains fill in a topwedge region formed by the variable thickness top spacer layer, inaccordance with an embodiment of the present invention;

FIG. 10 is a cross-sectional side view showing a plurality of thinnedvertical fins formed on a bottom source/drain layer with overetchedregions, in accordance with another embodiment of the present invention;and

FIG. 11 is a cross-sectional side view showing top source/drains formedon each of the vertical fins, where the top source/drains fill in a topwedge region formed by the variable thickness top spacer layer, and thebottom spacer layer forms dimpled portions in the overetched regions ofthe bottom source/drain layer, in accordance with another embodiment ofthe present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide field effect transistors(FinFET) devices with better gate edge-to-device channel positioning,and reduced gate-to-source/drain capacitances. The mismatch betweenvertical gate edge positioning relative to the junction of the verticalfin with the bottom source/drain can be reduced by tapering the bottomspacer thickness proximal to the adjoining vertical fin.

A bottom spacer layer with a non-uniform thickness is provided, wherethe bottom spacer layer can be tapered proximal to an adjoining verticalfin by shadowing the region with an overhanging hardmask. Theoverhanging hardmask can reduce the amount of bottom spacer layermaterial deposited by a directional deposition process adjacent to thevertical fin. The bottom spacer layer can have a lesser thickness in thebottom corners with the vertical fin(s), and a greater, more uniformthickness in the exposed regions between the hardmasks and verticalfins. The overlap capacitance between a gate structure and asource/drain can be reduced by the tapering.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: vertical finFETs, complementarymetal oxide silicon (CMOS) field effect transistors (FETs) formed bycoupled finFETs, and digital gate devices (e.g., NAND, NOR, XOR, etc.).

It is to be understood that aspects of the present invention will bedescribed in terms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of aspects of the presentinvention.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a cross-sectional side viewof a bottom source/drain layer formed on a substrate is shown, inaccordance with an embodiment of the present invention.

In one or more embodiments, a substrate 110 can be, for example, asingle crystal semiconductor material wafer or asemiconductor-on-insulator stacked wafer. The substrate 110 can includea support layer that provides structural support, and an activesemiconductor layer that can form devices. An insulating layer (e.g., aburied oxide (BOX) layer) may be between the active semiconductor layerand the support layer to form a semiconductor-on-insulator substrate(SeOI) (e.g., a silicon-on-insulator substrate (SOI)), or an implantedlayer can form a buried insulating material.

The support layer can include crystalline, semi-crystalline,micro-crystalline, nano-crystalline, and/or amorphous phases. Thesupport layer can be a semiconductor (e.g., silicon (Si), siliconcarbide (SiC), silicon-germanium (SiGe), germanium (Ge),gallium-arsenide (GaAs), cadmium-telluride (CdTe), etc.), an insulator(e.g.: glass (e.g. silica, borosilicate glass), ceramic (e.g., aluminumoxide (Al₂O₃, sapphire), plastic (e.g., polycarbonate,polyacetonitrile), metal (e.g. aluminum, gold, titanium,molybdenum-copper (MoCu) composites, etc.), or combination thereof.

The substrate 110 or active semiconductor layer can be a crystallinesemiconductor, for example, a IV or IV-IV semiconductor (e.g., silicon(Si), silicon carbide (SiC), silicon-germanium (SiGe), germanium (Ge)),a III-V semiconductor (e.g., gallium-arsenide (GaAs), indium-phosphide(InP), indium-antimonide (InSb)), a II-VI semiconductor (e.g.,cadmium-telluride (CdTe), zinc-telluride (ZnTe), zinc sulfide (ZnS),zinc selenide (ZnSe)), or a IV-VI semiconductor (e.g., tin sulfide(SnS), lead selenide (PbSb)).

In various embodiments, a bottom source/drain layer 120 can be formed onthe substrate, where the bottom source/drain layer 120 can be formed byepitaxial growth or heteroepitaxial growth on the top surface of thesubstrate 110. The bottom source/drain layer 120 can be a crystallinesemiconductor material, including, but not limited to, silicon (Si),silicon-germanium (SiGe), and germanium (Ge), that can include a dopant.The dopant can be an n-type dopant (e.g., phosphorus (P), arsenic (As))or p-type dopant (e.g., boron (B), gallium (Ga)). The dopant can beintroduced into the bottom source/drain layer 120 during formation(i.e., in situ) or after formation (i.e., ex situ), for example, by ionimplantation. Although the bottom source/drain layer 120 is shown asformed at the beginning, a bottom source/drain layer 120 can also beformed after the formation of vertical fins.

In various embodiments, the bottom source/drain layer 120 can have athickness in a range of about 20 nanometers (nm) to about 60 nm, or in arange of about 30 nm to about 50 nm, although other thicknesses are alsocontemplated.

FIG. 2 is a cross-sectional side view showing a vertical fin layer onthe bottom source/drain layer, and a plurality of fin templates formedon the vertical fin layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a vertical fin layer 130 can be formed onthe bottom source/drain layer 120, where the vertical fin layer 130 canbe formed by epitaxial growth or heteroepitaxial growth on the topsurface of the bottom source/drain layer 120.

In various embodiments, the vertical fin layer 130 can be asemiconductor material, including, but not limited to, a IV or IV-IVsemiconductor (e.g., silicon (Si), silicon carbide (SiC),silicon-germanium (SiGe), germanium (Ge)), a III-V semiconductor (e.g.,gallium-arsenide (GaAs), indium-phosphide (InP), indium-antimonide(InSb)), a II-VI semiconductor (e.g., cadmium-telluride (CdTe),zinc-telluride (ZnTe), zinc sulfide (ZnS), zinc selenide (ZnSe)), or acombination thereof. In various embodiments, the vertical fin layer 130can be the same material as the substrate 110 or active semiconductorlayer.

In one or more embodiments, a fin template layer can be formed on thevertical fin layer 130, where the fin template layer can be formed by ablanket deposition, for example, chemical vapor deposition (CVD), plasmaenhanced CVD (PECVD), physical vapor deposition (PVD) or a spin-onprocess, on the vertical fin layer 130. The fin template layer can bepatterned using spacer image transfer (SIT), lithography or otherpatterning techniques to form one or more fin templates 140 on the topsurface of the vertical fin layer 130.

In various embodiments, the fin templates 140 can be a hard mask, forexample, silicon oxide (SiO), silicon nitride (SiN), a siliconoxynitride (SiON), a silicon carbonitride (SiCN), a silicon boronitride(SiBN), a silicon borocarbide (SiBC), a silicon boro carbonitride(SiBCN), a boron carbide (BC), a boron nitride (BN), or combinationsthereof. In various embodiments, a thin (i.e., <3 nm) oxide layer can bebetween the top surface of the vertical fin layer 130 and the fintemplate 140.

In various embodiments, the fin templates 140 can have a width in arange of about 8 nm to about 30 nm, or about 10 nm to about 25 nm, orabout 12 nm to about 15 nm, although other widths are also contemplated.

In various embodiments, the fin templates 140 can be separated by adistance (between facing sidewalls) that determines the spacing ofsubsequently formed vertical fins. The fin templates 140 can beseparated by a distance in a range of about 15 nm to about 70 nm, orabout 20 nm to about 50 nm, or about 25 nm to about 35 nm, althoughother separation distances are also contemplated.

FIG. 3 is a cross-sectional side view showing a plurality of verticalfins formed on the bottom source/drain layer with the fin templates onthe vertical fins, in accordance with an embodiment of the presentinvention.

In various embodiments, one or more vertical fins 131 can be formed onthe bottom source/drain layer 120 with a fin template 140 on each of thevertical fins 131, in accordance with an embodiment of the presentinvention. The vertical fins 131 can be formed by a multiple patterningfabrication process, for example, a sidewall image transfer (SIT)process, a self-aligned double patterning (SADP) process, self-alignedtriple patterning (SATP) process, or a self-aligned quadruple patterning(SAQP). The vertical fins 131 may be formed by a direct write process ordouble patterning process using, for example, immersion lithography,extreme ultraviolet lithography, or x-ray lithography followed byetching.

In various embodiments, the vertical fins 131 can have a width in arange of about 8 nm to about 30 nm, or about 10 nm to about 25 nm, orabout 12 nm to about 15 nm, although other widths are also contemplated.The width of the vertical fins 131 can be the same as the width of thefin templates 140.

In various embodiments, the vertical fins 131 can have a height in therange of about 15 nanometers (nm) to about 100 nm, or about 15 nm toabout 50 nm, or about 50 nm to about 100 nm, or about 30 nm to about 70nm, although other heights are contemplated.

In various embodiments, the adjacent vertical fins 111 can be separatedby a distance in a range of about 20 nm to about 70 nm, or about 20 nmto about 50 nm, or about 30 nm to about 40 nm, although other distancesare also contemplated.

In various embodiments, a fin template 140 may be on each vertical fin132, where the fin template 140 is formed during the patterning process.The bottom source/drain layer 120 can be below the vertical fins 132,where the bottom source/drain layer 120 and vertical fin(s) 132 form avertical transport fin field effect transistor (VT FinFET).

FIG. 4 is a cross-sectional side view showing a plurality of thinnedvertical fins formed on the bottom source/drain layer with the fintemplates on the vertical fins, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the width of the vertical fins 131 can bereduced to form thinned vertical fin(s) 132, where the width of thevertical fins 131 can be reduced by using an isotropic etch, forexample, a wet chemical etch, a dry plasma etch, or a combinationthereof. In various embodiments, the width of the vertical fins 131 canbe reduced by oxidizing a portion of the vertical fins 131 and strippingthe oxide layer.

In various embodiments, the thinned vertical fins 132 can have a widthin a range of about 4 nm to about 28 nm, or about 6 nm to about 26 nm,or about 6 nm to about 20 nm, or about 5 nm to about 15 nm, althoughother widths are also contemplated. The width of the thinned verticalfin 132 can be less than the width of the fin template 140 on thethinned vertical fin, where a portion of the fin template 140 overhangsthe underlying thinned vertical fin.

In various embodiments, the fin template 140 can overhang the sides ofthe underlying thinned vertical fin by a distance of about 1 nm to about10 nm, or about 2 nm to about 5 nm, although other overhang distancesare also contemplated. The distance that the fin template 140 overhangsthe underlying thinned vertical fin 132 can be the same on all sides ofthe thinned vertical fin. The overhanging portion of the fin template140 can shadow the underlying surfaces and sidewalls of the verticalfin.

FIG. 5 is a cross-sectional side view showing a non-uniform thicknessbottom spacer layer formed on the bottom source/drain layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, a bottom spacer layer 150 can be formed onthe exposed surface of the bottom source/drain layer, where the bottomspacer layer 150 can be formed by a directional deposition, for example,a high density plasma (HDP) deposition, physical vapor deposition (PVD),or a gas cluster ion beam (GCIB) deposition. The bottom spacer layer 150can also be formed by non-conformal deposition techniques, such asplasma enhanced chemical vapor deposition (PECVD). The material of thebottom spacer layer 150 can be preferentially formed on surfacessubstantially perpendicular to the direction of the deposition, whilethe surfaces substantially parallel with the direction of deposition canremain essentially uncovered. The overhanging portions of the fintemplates 140 can shadow the regions of the bottom source/drain layer120 adjacent to the thinned vertical fins 132, where less material maybe deposited on the shadowed region(s) depending on the extent of thebeam divergence (i.e., increase in beam diameter or radius with distancefrom the beam source or aperture) of the deposition process (e.g., ionbeam, physical vapor trajectory, gas cluster trajectory). Spacermaterial includes suitable dielectric material, but is not necessarilylimited to, silicon boron nitride (SiBN), siliconborocarbonitride(SiBCN), silicon oxycarbonitride (SiOCN), SiN or SiO₂.

In various embodiments, the bottom spacer layer 150 can have anon-uniform thickness, where the thickness of the bottom spacer layer150 can vary in a direction parallel with the width of the thinnedvertical fins 132 and transverse to the long axis of the thinnedvertical fins. The thickness of the bottom spacer layer 150 can taper inthe direction towards the thinned vertical fins. The amount that thethickness varies with the distance from the sidewall or end wall of athinned vertical fin 132 can depend on the distance that the fintemplate 140 overhangs the sides of the thinned vertical fin and thebeam divergence of the deposition process.

In one or more embodiments, the bottom spacer layer 150 can have athickness in the range of about 5 nm to about 10 nm, or about 10 nm toabout 20 nm, in the region between adjacent fin templates 140, althoughother thicknesses are also contemplated. The thickness of the bottomspacer layer 150 can vary from a minimum in a range of about 5 nm toabout 15 nm directly adjoining the sidewall or end wall of the thinvertical fin 132 to the thickness in the region between adjacent fintemplates 140. The amount that the thickness of the bottom spacer layer150 tapers between the sidewall or end wall of the thin vertical fin 132and the thickness in the region between adjacent fin templates 140, andthe cross-sectional profile of the tapered region, can depend on thedistance that the fin template 140 extends passed the sidewall or endwall of the thin vertical fin (overhangs) the underlying thinnedvertical fin and the beam divergence profile.

In various embodiments, a bottom wedge region 152 can be formed adjacentto the thinned vertical fin(s) 132 by the tapering of the variablethickness bottom spacer layer 150. The bottom wedge region 152 canexpose a portion of the adjacent thinned vertical fin 132 below the topsurface of the bottom spacer layer 150. The reduced thickness of thebottom spacer layer adjacent to the thinned vertical fin 132 reduces theamount that the overlap between a subsequently formed gate structure andbottom source/drain-to-device channel junction can vary. The thickerposition of bottom spacer between the subsequently formed gate and thebottom source/drain region can help reduce the overlap capacitance. Thesubstantially thinner bottom spacer layer adjacent to the thinnedvertical fin 132 can help achieve better gate control on the device dueto the closer distance between the gate structure and the channel andsource/drain junction.

In various embodiments, an isotropic etch, for example a wet chemicaletch, or dry plasma etch, can be used to remove extraneous materialsfrom the sidewalls and endwalls of the thinned vertical fins 132 and fintemplates 140.

FIG. 6 is a cross-sectional side view showing a gate dielectric layerformed on the exposed surfaces of the thinned vertical fins and variablethickness bottom spacer layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a gate dielectric layer 160 can be formed onthe exposed surfaces of the bottom spacer layer 150, thinned verticalfins (132, and fin templates 140. The gate dielectric layer 160 can beformed by a conformal deposition, for example, atomic layer deposition(ALD) or plasma enhanced ALD (PEALD).

In one or more embodiments, a gate dielectric layer 160 can bedielectric material including, but not limited to, silicon oxide (SiO),silicon nitride (SiN), silicon oxynitride (SiON), boron nitride (BN),high-k dielectric materials, and combinations thereof. Examples ofhigh-k materials include but are not limited to metal oxides, such as,hafnium oxide (HfO), hafnium silicon oxide (HfSiO), hafnium siliconoxynitride (HfSiON), lanthanum oxide (LaO), lanthanum aluminum oxide(LaAlO), zirconium oxide (ZrO), zirconium silicon oxide (ZrSiO),zirconium silicon oxynitride (ZrSiON), tantalum oxide (TaO), titaniumoxide (TiO), barium strontium titanium oxide (BaSrTiO), barium titaniumoxide (BaTiO), strontium titanium oxide (SrTiO), yttrium oxide (YO),aluminum oxide (AlO), lead scandium tantalum oxide (PbScTaO), and leadzinc niobate (PbZnNbO). The high-k material may further include dopantssuch as lanthanum, aluminum, magnesium, or combinations thereof.

In various embodiments, the gate dielectric layer 160 can have athickness in the range of about 7 Å to about 50 Å, or about 7 Å to about30 Å, or about 1 nm to about 2 nm, although other thicknesses arecontemplated. In various embodiments, the thickness of the gatedielectric layer 160 can be less than or equal to the distance that thefin template 140 overhangs the underlying thinned vertical fin 132. Aportion of the gate dielectric layer 160 can be formed in a bottom wedgeregion 152 adjacent to the thinned vertical fin 132.

FIG. 7 is a cross-sectional side view showing a gate fill layer formedon the gate dielectric layer, where the gate fill layer fills in abottom wedge region formed by the variable thickness bottom spacerlayer, in accordance with an embodiment of the present invention.

In one or more embodiments, a gate fill layer 170 can be formed on thegate dielectric layer 160, where the gate fill layer 170 can be formedby any suitable deposition technique, including but not limited to, CVD,PECVD, metal-organic CVD (MOCVD), sputtering, plating, evaporation, ionbeam deposition, electron beam deposition, laser assisted deposition,chemical solution deposition, or any combination of those methods. Thegate fill layer 170 can fill in the bottom wedge regions 152 adjacent tothe thinned vertical fins 132.

In one or more embodiments, the gate fill layer 170 can be a conductivematerial, including, but not limited to, doped polycrystalline oramorphous silicon, germanium, silicon-germanium, a metal (e.g.,tungsten, titanium, tantalum, ruthenium, zirconium, cobalt, copper,aluminum, platinum, silver, gold), a conducting metallic compoundmaterial (e.g., tantalum nitride, titanium nitride, tantalum carbide,titanium carbide, titanium aluminum carbide, tungsten silicide, tungstennitride, ruthenium oxide, cobalt silicide, nickel silicide), carbonnanotubes, conductive carbon, graphene, or any suitable combination ofthese materials. The conductive gate fill layer 170 may further comprisedopants that are incorporated during or after deposition.

In various embodiments, a portion of the gate fill layer 170 thatextends above the fin templates 140 can be removed using achemical-mechanical polishing (CMP) to provide a smooth, flat surface.

FIG. 8 is a cross-sectional side view showing a variable thickness topspacer layer formed on the gate fill layer and gate dielectric layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, the height of the gate fill layer 170 can bereduced, for example, by using a directional etch (e.g., reactive ionetch (RIE)), where the height of the gate fill layer 170 can be reducedbelow the bottom surface of the fin templates 140, such that an upperportion of the thinned vertical fins 132 are exposed. An additionalisotropic etch (e.g., wet chemical etch) may be applied to remove theshadowed regions of the gate fill layer 170 and gate dielectric layer160 adjacent to the thinned vertical fins 132 by the overhangingportions of the fin templates 140.

In various embodiments, the reduction in height of the gate fill layer170 can expose a portion of the gate dielectric layer 160 on the upperportions of the thinned vertical fins. The exposed portion of the gatedielectric layer 160 can be removed using an isotropic etch (e.g., wetetch) to expose the underlying thinned vertical fins 132.

In one or more embodiments, a top spacer layer 180 can be formed on theexposed surface of the gate fill layer 170, where the bottom spacerlayer 150 can be formed by a directional deposition, for example, a highdensity plasma (HDP) deposition, physical vapor deposition (PVD), or agas cluster ion beam (GCIB) deposition.

In various embodiments, the top spacer layer 180 can have a non-uniformthickness, where the thickness of the top spacer layer 180 can vary in adirection parallel with the width of the thinned vertical fins 132 andtransverse to the long axis of the thinned vertical fins. The amountthat the thickness varies with the distance from the sidewall or endwall of a thinned vertical fin 132 can depend on the distance that thefin template 140 overhangs the sides of the thinned vertical fin and thebeam divergence of the deposition process.

In one or more embodiments, the top spacer layer 180 can have athickness in the range of about 5 nm to about 10 nm, or about 10 nm toabout 20 nm, in the region between adjacent fin templates 140, althoughother thicknesses are also contemplated. The thickness of the top spacerlayer 180 can vary from a minimum in a range of about 2 nm to about 15nm, or about 5 nm to about 10 nm directly adjoining the sidewall or endwall of the thin vertical fin 132 to the thickness in the region betweenadjacent fin templates 140. The thickness of the top spacer layer 180can be greater than zero to prevent electrical shorting of a topsource/drain to the gate structure.

The bottom spacer and top spacer formation can be similar, given theshadowing effects from the overhanging portions of the fin templates140. The thinnest portion of the bottom and top spacer layer can be asthin as 1 nm.

In various embodiments, a top wedge region 182 can be formed adjacent tothe thinned vertical fin(s) 132 by the tapering of the variablethickness top spacer layer 180. The top wedge region 182 can expose aportion of the adjacent thinned vertical fin 132 below the top surfaceof the top spacer layer 180 and fin templates 140.

FIG. 9 is a cross-sectional side view showing top source/drains formedon each of the vertical fins, where the top source/drains fill in a topwedge region formed by the variable thickness top spacer layer, inaccordance with an embodiment of the present invention.

In one or more embodiments, the fin templates 140 can be removed fromthe thinned vertical fins 132 using a selective isotropic etch (e.g., wechemical etch) to expose the top surfaces of the thinned vertical fins.

In one or more embodiments, a top source/drain 190 can be formed on theexposed upper portions of the thinned vertical fins 132, where the topsource/drains 190 can be formed by epitaxial or heteroepitaxial growthon the thinned vertical fins 132. The top source/drains 190 can be acrystalline semiconductor material, including, but not limited to,silicon (Si), silicon-germanium (SiGe), and germanium (Ge), that caninclude a dopant.

In various embodiments, the top source/drains 190 can fill in the topwedge region 182.

FIG. 10 is a cross-sectional side view showing a plurality of thinnedvertical fins formed on a bottom source/drain layer with overetchedregions, in accordance with another embodiment of the present invention.

In various embodiments, a portion of the bottom source/drain layer 120between adjacent fin templates 140 can be partially removed to formdimpled portions 124, where, during the fin RIE process, a slightoveretch can form the recessed dimpled portions 124 in the bottomsource/drain layer 120. In various embodiments, the bottom source/drainlayer 120 can be partially removed using a selective directional etch(e.g., RIE). A small flat portion of bottom source/drain (unetched) atfin corner after RIE vertically underneath the fin hardmask.

FIG. 11 is a cross-sectional side view showing top source/drains formedon each of the vertical fins, where the top source/drains fill in a topwedge region formed by the variable thickness top spacer layer, and thebottom spacer layer forms dimpled portions in the overetched regions ofthe bottom source/drain layer, in accordance with another embodiment ofthe present invention.

In various embodiments, a variable thickness bottom spacer layer 150 canbe formed on the bottom source/drain layer 120, where the bottom spacerlayer 150 can fill in the dimpled portions of the bottom source/drainlayer 120.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” used herein,specify the presence of stated features, integers, steps, operations,elements and/or components, but do not preclude the presence or additionof one of more other features, integers, steps, operations, elements,components and/or groups thereof.

Spatially relative s such as “beneath,” “below,” “lower,” “above,”“upper,” like, can be used herein for ease of description to describeone element's or feature's relationship to another element(s) orfeature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used be can be interpreted accordingly. In addition, it willalso be understood that when a layer is referred to as being “between”two layers, it can be the only layer between the two layers, or one ormore intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming a fin field effect transistordevice, comprising: forming a vertical fin on a bottom source/drainlayer; reducing the width of the vertical fin to form a thinned verticalfin; and depositing a bottom spacer layer on the bottom source/drainlayer, wherein the bottom spacer layer has a non-uniform thickness thattapers in a direction towards the thinned vertical fin.
 2. The method ofclaim 1, wherein the vertical fin has a width in a range of about 10 nmto about 30 nm, and the thinned vertical fin has a width in a range ofabout 5 nm to about 15 nm.
 3. The method of claim 1, wherein the bottomspacer layer is formed by a directional deposition.
 4. The method ofclaim 3, wherein the bottom source/drain layer is partially etched by adirectional reactive ion etch to form a recessed portion between atleast two adjacent vertical fins.
 5. The method of claim 1, furthercomprising forming a gate dielectric layer on the exposed surfaces ofthe one or more thinned vertical fins and the bottom spacer layer. 6.The method of claim 5, further comprising forming a gate fill layer onthe gate dielectric layer.
 7. The method of claim 6, further comprisingforming a top spacer layer on the gate fill layer, wherein the topspacer layer has a non-uniform thickness that tapers in a directiontowards the thinned vertical fins.
 8. The method of claim 7, furthercomprising forming a top source/drain on the thinned vertical fin. 9.The method of claim 8, wherein the bottom source/drain layer has dimpledportions.
 10. The method of claim 8, wherein the bottom spacer layerfills in the dimpled portions of the bottom source/drain layer.
 11. Amethod of forming a fin field effect transistor device, comprising:forming a vertical fin with a fin template on the vertical fin on asubstrate; reducing the width of each of the vertical fins to form oneor more thinned vertical fins, wherein at least a portion of the fintemplate overhangs the sides of the underlying thinned vertical fin; anddepositing a bottom spacer layer on the bottom source/drain layer usinga directional deposition, wherein the bottom spacer layer has anon-uniform thickness that tapers in a direction towards the thinnedvertical fins.
 12. The method of claim 11, wherein the vertical fin hasa width in a range of about 10 nm to about 30 nm, and the thinnedvertical fin has a width in a range of about 5 nm to about 15 nm. 13.The method of claim 11, wherein the directional deposition is a highdensity plasma (HDP) deposition, physical vapor deposition (PVD), or agas cluster ion beam (GCIB) deposition.
 14. The method of claim 11,further comprising forming a gate dielectric layer on the exposedsurfaces of the one or more thinned vertical fins and the bottom spacerlayer.
 15. The method of claim 14, wherein the gate dielectric layer athickness in a range of about 7 Å to about 50 Å.
 16. A method of forminga fin field effect transistor device, comprising: forming a bottomsource/drain layer on a substrate; forming a vertical fin with a fintemplate on the vertical fin on the bottom source/drain layer; reducingthe width of the vertical fin to form a thinned vertical fin, wherein atleast a portion of the fin template overhangs the sides of theunderlying thinned vertical fin; depositing a bottom spacer layer on thebottom source/drain layer using a directional deposition, wherein thebottom spacer layer has a non-uniform thickness that tapers in adirection towards the thinned vertical fins; forming a gate dielectriclayer on the exposed surfaces of the one or more thinned vertical finsand the bottom spacer layer using a conformal deposition; and forming agate fill layer on the gate dielectric layer.
 17. The method of claim16, further comprising forming a top spacer layer on the gate filllayer, wherein the top spacer layer has a non-uniform thickness thattapers in a direction towards the thinned vertical fin.
 18. The methodof claim 17, further comprising forming a top source/drain on thethinned vertical fin, wherein the top source/drain fills in a top wedgeregion adjacent to each of the one or more thinned vertical fins. 19.The method of claim 18, wherein the thinned vertical fin has a width ina range of about 5 nm to about 15 nm.
 20. The method of claim 19,wherein the bottom spacer layer is made of a dielectric materialselected from the group consisting of silicon boron nitride (SiBN),siliconborocarbonitride (SiBCN), silicon oxycarbonitride (SiOCN), SiNand SiO₂.